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PAD PREPARATION:
Prior to replacing the TSOP it is recommended that the main
board pads be cleaned of old solder. Using fluxfrom a syringe or
pen (for example Kester #186) and de-soldering braid the pads
should be restored to a cleanflat surface. This will allow the
array of pins on each side of the TSOP to sit flatly on the
board.
CHIP PLACEMENT:
The vacuum hand tool viewed in the photograph may be used to
manipulate and control the preciseplacement of the component. The
chip should be placed such that the correct orientation is observed
(doton board with dot indentation on TSOP) and with the pins
correctly aligned with their respective pads. Thecomponent should
not be glued into place. A magnifying glass is recommended.
SECURING THE TSOP:
Flux should be liberally applied to the pad and pin area. A
strand of rosin core solder should be placed near acorner of the
TSOP. While holding the component in place with the vacuum tool in
one hand, the other handis free to direct a hot and wide soldering
iron tip (for example 700 degree 3mm screwdriver tip) toward
thesolder strand. The particular objective being to tack the
opposite corners of the chip with solder to hold theTSOP in place.
It is perfectly acceptable to bridge the solder over several
pins.
SOLDER BRIDGING THE PIN ARRAY:
A magnifying glass should be used to verify correct pin
orientation and alignment. Hover the iron above astrand of solder
directly above each row of pins and pads so that the molten product
flows abundantly intothe component footprint area. Bridge the
solder completely across both rows of pins. Reapply flux to thearea
and reheat the pin and pad area. The bottom of the pins must
receive an adequate supply of solder toensure correct bonding.
Solder Bridging and Re-flowing
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After the flux and solder have been heated and the molten
product has been evenly dispersed in the footprintarea, a bridge of
solder is likely to be present across the two pin arrays. This, of
course, was intentional atfirst but is no longer desirable. This
excessive solder would destroy the circuitry if it was powered-up.
Thenext objective, then, is to remove the solder bridge but leave
the solder which has collected between thepins and pads.
In fact this is the 'trick' to this entire process.
Shorting some or all pins with solder and then removing the
bridges with solder wick!
Using a generous application of flux (Kester #186) and a fresh
length of de-soldering braid the excessivesolder is removed leaving
a perfectly attached TSOP.
To accomplish this, place a length of braid across the pin
array. Gently touch the braid (solder wick) directlywith the
soldering iron tip (700 degree 3mm screwdriver). The solder will
reflow at this point and becomeabsorbed by the braid. Run the hot
iron tip along the braid length so as to completely remove the
solderbridge. It may be necessary to repeat this using fresh
de-soldering braid. If solder-alloy breaks down andsolder product
remains, reapply fresh rosin core solder and repeat the
flux/de-solder process. Care must beexercised not to damage the
pins and the PC board pads. Do not 'push' the soldering tool and
avoid excessiveheat. This is a learned skill so practice is
required.
Use a magnifying glass to inspect the pins for spittle, which
may cause shorting or pin-to-pin bridging. It isprudent to clean
the area with a flux remover. The cleaning fluid will evaporate but
a clean absorbent clothmay help the process along.
When satisfied, a power-on test should be commenced. The unit
should come to life as before. If nothinghappens likely a pin or
two is not making contact. If this is the case unplug the receiver
and test the pinswhile looking through a magnifying glass and by
using an EXACTO blade gently push each pin to confirm asoldered
contact. As an alternative to this reflux the area and reapply
solder. Bridge the area once againand use flux and de-soldering
braid to remove the bridge. If required, repeat this process until
all pins are
correctly attached. THE TSOP PINS ARE VERY FRAGILE. SHOULD THEY
BECOME DISTORTED AND CORRECTIONBECOMES NECESSARY THEY MAY PROVE TO
BE UNRELIABLE.
Once the unit comes to life when powered up it is wise to test
board integrity. To do this press on the mainboard gently in the
area around the TSOP. Often 'cold-soldering' causes the receiver to
functionintermittently.
Before mating the chassis to the cover it is wise to do a final
and complete test by hooking the receiver tothe dish and television
monitor.
